308A HVAC Ductwork Systems 5

Question 1

What is the standard duct sealant class designation system used in SMACNA?

Accepted Answer

Seal Class A (all seams and joints), B (transverse joints and seams), and C (transverse joints only)

Answer

SMACNA defines Seal Class A (most stringent — all seams, joints, and wall penetrations), B (transverse joints and seams), and C (least stringent — transverse joints only). Higher-pressure systems require more sealing.

Question 2

What is a 'take-off' fitting in HVAC ductwork?

Accepted Answer

A branch connection fitting that diverts a portion of airflow from a main duct to a branch duct

Answer

A take-off is a branch fitting that connects a smaller branch duct to a larger main duct, diverting a portion of the airflow. Common types include conical, straight, and 45-degree take-offs.

Question 3

What is the recommended hanger spacing for rectangular ductwork up to 48 inches wide?

Accepted Answer

Every 8 to 10 feet maximum

Answer

SMACNA recommends maximum hanger spacing of 8 to 10 feet for rectangular duct up to 48 inches wide. Larger or heavier ducts require closer spacing and stronger hanger materials.

Question 4

What is the purpose of a 'volume damper' versus a 'splitter damper' in a duct system?

Accepted Answer

A volume damper restricts total airflow in a single duct, while a splitter damper divides airflow between two branches

Answer

Volume dampers (butterfly or opposed blade) regulate total airflow through a single duct section. Splitter dampers are positioned at branch take-offs to proportionally divide airflow between the main and branch ducts.

Question 5

What is the effect of a duct system having too many sharp 90-degree elbows?

Accepted Answer

Increased pressure drop, reduced airflow, higher energy costs, and potential noise problems

Answer

Sharp 90-degree elbows create significant turbulence and pressure drop. Each adds equivalent length to the system, reducing total airflow capacity, increasing fan energy consumption, and generating noise.

Red Seal Sheet Metal 308A Practice Test

Red Seal Sheet Metal 308A Practice Test

308A HVAC Ductwork Systems 5